Governmental regulations throughout most of the world require the use of certain colors of light for automotive signaling functions. In particular, red light having specific chromaticity boundaries is typically required for rear tail lamps and brake lamp signaling, and can be used as well for rear turn signals. To achieve this red light, clear incandescent lamps are typically used in a conjunction with a red filter lens. However, the use of a red exterior filter lens can limit the aesthetic styling of the vehicle. Also, in the event the lens is broken open, exposing the lamp, the non-red wavelengths of the emitted light may no longer be filtered out.
Accordingly, various approaches for producing red incandescent lamps have been investigated and proposed over the years. The most common approach is to apply a red pigment to the exterior surface of a standard clear glass lamp. However, while pigments that produce suitable filtering of the light have been known for years, they are not commonly used in automotive applications because the level of pigment concentration required to obtain the proper coloration of the light is so high that the resulting luminance level of the emitted light is too low.
It is therefore an object of this invention to provide an automotive incandescent lamp that provides a red colored light output which meets the applicable governmental requirements for both spectral content and intensity.